Robert and Cora - Downton Abbey
Originally, Robert only married Cora for her money. But eventually, he truly falls in love with her and they start a family.
Amy and Karma - Faking It
Amy and Karma pretended to be in love to boost their popularity. However, things got intense when Amy realized that she was in love with her best friend and she was no longer faking it.
Emma and Ethan - The Lying Game
This one's different, but it works. Sutton and Ethan were together until Emma poses as her twin sister and no one loops Ethan in on the switch. However, Ethan figures it out after kissing Emma and they end up falling for each other. They go public with their relationship at a school dance, but everyone thinks that Sutton and Ethan are the ones dating.
Val and Vic - What I Like About You
Val and Vic get married by accident during one very drunken night. Val is originally outraged and wants nothing to do with Vic. Towards the end of the series, she falls in love with him and they get remarried when they find out the first marriage wasn't valid.
Skye and Ward - Agents of S.H.I.E.L.D.
Ward was working for Hydra and lying to Skye and the rest of the team for the entirety of Season 1. The last thing he expected to happen, was to fall for Skye while he was undercover.